Catalytic cleaning processes can be used to partially or completely remove pollutants from the exhaust gas of an internal combustion engine. Specifically, exhaust gas cleaning may be achieved using a reducing agent that reduces one or more pollutants, for example, NOx, in the exhaust gas.
In order to reduce exhaust gas emissions from an internal combustion engine, the reducing agent (e.g. a reagent such as urea solution) can be sprayed into an exhaust passage using an injection device, as shown, for example, in EP1878887. Typically, the activity of the reducing agent is triggered on contact with a catalyst downstream from the point of injection. A Selective Catalytic Reduction (SCR) device performs selective catalytic reduction of nitrogen oxide (NOx) using ammonia (derived from the urea). An injection device, mounted to the passage of an exhaust system, is used to inject the urea into the exhaust flow. A slip catalyst is located downstream of the SCR device to clean up any unreacted ammonia. A diesel particulate filter is also provided to reduce the level of particulate matter and soot that is entrained in the exhaust gas flow and which is not reduced by the SCR device.
It is known for the injection device for reagent to include an outward opening poppet valve to produce a well atomised conical spray. The circular cross section of the projected spray is well suited to the cylindrical shape of the circular exhaust pipe (i.e. having a circular cross section). However, more recently it has been found to be desirable to move the spray point into the exhaust passage closer to the engine in order to allow the SCR catalyst to heat up faster. In order to join the catalysts and the particulate filters in as compact a form as possible, the flow sections of the exhaust passage between them need to be wider in one direction than the other.
It is therefore one object of the invention to provide an injection device which is suitable for injecting a reagent into an exhaust passage having a non-circular cross-section.